Remotely-located cold head for stirling cycle engine



June 15, 1965 J. G. DAUNT REMOTELY-LOCATED COLD HEAD FOR STIRLING CYCLE ENGINE Filed April 7, 1964- 2 Sheets-Sheet 1 INVENTOR. JOHN G. DAUNT 72: ATTORNE June 15, 1965 J. G. DAUNT 3,188,822

REMOTELY-LOGATED COLD HEAD FOR STIRLING CYCLE ENGINE Filed April '7, 1964 2 Sheets-Sheet 2 INVENTOR.

JOHN G. DAUNT ATTORNEY United States Patent Oii ice 3,188,822 Patented June 15, 19.65

3,188,822 REMOTELY-LGCATED CULT) HEAD FUR STIRLING CYCLE ENGINE John G. Daunt, Columbus, Ohio, assignor to Maiaker Laboratories, Inc., High Bridge, N.J., a corporation of New Jersey Filed Apr. 7, 1964, Ser. No. 357,954 4 Claims. (Cl. 626) This invention deals with a cold head attachment to a cryogenic engine operating on the Stirling cycle, or modifications thereof. More specifically, it relates to a flexible, thin wall, small diameter tubing extension connected to the heads of the compression and expansion cylinders. Said extension also may incorporate therein the regenerator usually made an integral portion of the engine.

In Patent 3,074,244, there is described a cryogenic engine operating on the Stirling cycle, or modification thereof. Such an engine can be used to reach low temperatures in the neighborhood of 30 K., or even lower. In actual application, such an engine has a perforated expansion cylinder head and a conduit connecting the expansion and compressor heads (beyond the regenerator). The coldest portion of the engine is this connecting conduit. If the refrigeration is to be transferred to a location remotely situated from the engine, a flexible conductive cable is attached to said conduit and is used to transfer the heat thereto.

It has now been found that the cold produced by the engine may be concentrated in a flexible small bore thin walled tubing connected between the cylinder heads. Also, it has been found that the regenerator, instead of being located at the end of the compression cylinder, also may be located remotely from the engine in the extension already described.

The invention will be more readily understood by reference to the accompanying drawings in which a preferred embodiment is described, and in which FIGURE 1 presents a cross-sectional side view of an engine of the present invention, incorporating a refrigerating extension heretofore referred to. FIGURE 2 illustrates a side view of the upper portion of such an engine, partly in cross section, showing the incorporation of the regenerator in said refrigerating extension. Similar numerals refer to similar parts in the various figures.

Referring again to the drawings, numeral 3 represents generally a cryogenic engine operating on the Stirling cycle, or modifications thereof, such as that described in Patent 3,074,244, which shows such an engine having cylinders disposed in parallel, or other types of engines operating on a Stirling cycle. In this engine, shaft 4 is driven by an electric motor (not shown) which is powered by a suitable source (not shown). Shaft 4 is connected to cranks 5 and 5' on which are mounted piston rods 6 and 7, respectively, having a phase angle of about 90. These are disposed within housing or crankcase 8.

Projecting at right angles from the side wall of housing 8 is compressor cylinder 9, in which rides compressor piston 10 attached to piston rod 7. The working gas (e.g., helium) which is compressed by piston 10 passes through perforated head 11 and regenerator 12 disposed on the end of cylinder 9. Regenerator 12 (disposed in extension 16 of cylinder 9) is filled with a metallic network, such as a metal wool of high heat capacity.

Also projecting from the side wall of housing 8 is expander cylinder 13 in which reciprocates expander piston 14 attached to the end of connecting rod 6. Attached to the top of piston 61 is a piston extension 14', made of insulating material, such as resin-molded fiber, fitting loosely in cylinder 13, and in extension 15 of cylinder 13. Cylinder head 17 encloses cylinder extension 15, while head 18 encloses cylinder extension 16.

Entering head 17, and connected thereto at 20, in outside-sealing relation, is end 19' of tube 19. This tube 19 projects for any desired distance beyond the cylinder heads, and it preferably projects in the form of a loop or U-end 19". The other end 19a of tube 19 penetrates head 18 at 21, and is connected thereto, in outside-sealing relation. Tube 19 is preferably of small diameter and thin wall. It may be flexible so as to be bent into the shape or to the direction desired. It is preferable to make tube 19 out of stainless steel with terminal cold end 19" of high conductivity metal such as copper or copper-clad metal. The inner diameter of tube 19 may be about to about 4", depending upon the size of the engine, and its length may be 1-2 feet, or even more. The cylinder upper portions and tube 19 are insulated with insulation 22, it being understood that the insulation at 19" is re moved to connect end 19 with the object to be cooled.

In operation, the working gas cycles between the two cylinders, and passes through tube 19, cooling end 19" to the desired temperature. Although there is loss of chiciency by use of such a tube 19, still adequate cooling may be obtained for uses remotely situated from the engine. For example, such an engine, without tube 19, but with a normal conduit cold head, can deliver a 9 watt refrigerating power at 77 K. With a 12" long tube 19, such as that shown in FIG. 1, the refrigeration capacity is 2 watts at 77 K., for a total input power of watts while using helium at a pre-operational filling pressure of 250 p.s.i. Fins 23 on the cylinders serve to air cool the unit.

A more ellicient arrangement than that shown in FIG. 1 is depicted in FIG. 2. Here, the regenerator 12 is located in tube 19, and the dead volume associated with a small-bore U-tube is divided, more or less equally, into dead volume at low temperature and dead volume at compressor temperature. Since dead volume at compressor temperature is less disadvantageous to the efficiency of operation than dead volume at low temperature, the system depicted in FIG. 2 has a higher efiiciency than that shown in FIG. 1.

I claim:

1. In a cryogenic engine operating on the Stirling type cycle, and having'a compressor cylinder head and an expander cylinder head, between which heads a working gas is cycled and cooled, the improvement, comprising,

a small diameter tube connected to and extending outwardly beyond said heads, and serving as the refrigeration-transmitting means for such engine.

2. A cryogenic engine according to claim 1 in which the tube is a U-tube, the terminal end of which is made of a metal of high conductivity.

3. In a cryogenic engine operating on the Stirling type cycle, and having a regenerator, a compressor cylinder head and an expander cylinder head, between which References Cited bythe Examiner v v UNITED STATES PATENTS Du Pre 626 Finkelsteins 626 Meijer 626 Flynn 626 WILLIAM J. WYE, Primary Examiner. 

1. IN A CRYOGENIC ENGINE OPERATING ON THE STIRLING TYPE CYCLE, AND HAVING A COMPRESSOR CYLINDER HEAD AND AN EXPANDER CYLINDER HEAD, BETWEEN WHICH HEADS A WORKING GAS IS CYCLED AND COOLED, THE IMPROVEMENT, COMPRISING 